62 APPLIED BACTERIOLOGY 



(23) Silica Jelly.— This novel and ingenious preparation, 

 which is wholly destitute of organic matter, was devised 

 by Klihne, and was used by him and Frankland in their 

 researches on the organisms of ' nitrification,' which will 

 not grow on an organic medium. In this preparation the 

 gelatinous consistency is obtained by means of dialysed 

 silicic acid. The method of preparation is as follows : Two 

 solutions of the following composition are prepared : 



(a) Ammonium sulphate, 0-4 (&) Potassium phosphate, O'l 



gramme. gramme. 



Magnesium sulphate, 0-05 Sodium carbonate, 0-75 



gramme. gramme. 



Calcium chloride, trace. Distilled water, 50"0 c.c. 



Distilled water, 50"0 c.c. 



These two solutions are rendered sterile by the usual 

 method, after which they are mixed. 



A sterile solution of dialysed silicic acid is now prepared 

 as follows : A solution of potassium or sodium silicate is 

 poured into dilute hydrochloric acid ; the mixture is then 

 placed in a dialyser, the outside of which is kept surrounded 

 with running water during the first day, and subsequently 

 with distilled water, which is frequently changed until it 

 yields no trace of turbidity with silver nitrate, thus showing 

 the whole of the chlorides to have been extracted. The 

 contents of the dialyser, if the solution of alkaline silicate 

 originally employed was not too strong, will be quite 

 clear. This liquid is then poured into a flask and con- 

 centrated by boiling until it is of such a strength that 

 it is found that, on cooling a little of the solution and 

 mixing it with one-third of the above mixed alkaline solu- 

 tions, it readily gelatinises on standing. When the solution 

 of silicic acid is found to give this result, it is cooled, and 

 one-third to one-half of its volume of the mixed alkaline 



